SEALING MEMBER

Abstract: A seal (6) for cable splices (1) is formed of a first element with an adhesive external surface (10) and springy and/or elastic second element, which can store energy to maintain the first element in contact with a surface to be sealed.

Description: Sealing Member The invention relates to a sealing system comprising an elastomeric or other seal preferably in block or strip form, and preferably for sealing a cable splice case. Providing casings, containers etc., more particularly cable sleeves, or other splice cases the internal space of which must be protected as durably as possible against environmental influences, especially dampness, is familiar. Examples exist where casing closing elements, such as doors and lids are present or where elements enter the casings, such as ingoing cables in the case of cable sleeves. In the older solutions it was known to apply an insulating mastic etc. in excessive quantities to the cable input area, between two separate casing halves. When the casing halves were closed around the cable splice the mastic was deformed around the ingoing cables to form a seal. One problem of such mastics, for example, those based on butyl rubber, is that they creep under temperature cycling. As a result, therefore, of different thermal expansion coefficients and different heat transfer values between the sealing surfaces and the mastic, leakages occur. In order to avoid such problems, heat-shrinkable sleeves were used around cable inlets which shrink when heat is applied and thereby seal tightly to the casing inlet and to the cable passing through it. Hot-melt adhesive coatings on the heat-shrink sleeves ensured the necessary adhesion. Although this technology has considerable advantages, one of its disadvantages is that a flame always has to be used for shrinking, which often leads to local problems on site. The aim of the invention is to overcome the problems of the prior art, and in particular to provide a seal that is simple to use and can accommodate the varying forces that result from temperature and pressure cycling. To this end we have devised a seal of a particular shape and preferably having a first element having an adhesive external surface and a springy or elastic second element which can store energy thus maintaining the first element in contact with a surface (such as a cable and/or a splice case) to be sealed. Thus, the invention provides a seal shaped to have one or more of the following characteristics: (a) a cable and/or housing mating surface is tapered and/or frustoconical thus allowing cables of different sizes to be sealed within a housing of given inlet size; (b) a seal has a substantially convex outer surface, such as circular (which term includes semi- or other part circular) or polygonal such as pentagonal, hexagonal, heptagonal or octagonal such that externally applied compressive forces (resulting for example from closure of a housing in an inlet of which the seal is provided) are concentrated or focused on a cable within the seal; and (c) the seal comprises two parts, each having first and second partial cavities therein, such that the parts can be assembled with the two first parts or the two second parts mutually aligned, the two first partial cavities together defining an inlet of different size or shape than the two second partial cavities together. The seal preferably has an adhesive outer surface provided by a first element (which may be a layer that is attached to the remainder of the seal, or that is integral with it) and springy or elastomeric second element that can in general store energy thereby maintaining the first element in contact with the cable or splice case inlet etc. In this way it is possible to accommodate expansion and contracting of the various parts of the splice case, due for example to temperature or pressure cycling. Adhesion to the various surfaces can therefore be maintained. The elasticity on the one hand and adhesiveness on the other can also result in the seal being pressed into uneven areas, thus increasing the sealing effect even further. The level of adhesiveness will be chosen depending on the particular end use, and it need not be high. The surface may be merely slightly tacky or may merely "wet" the surface to which it is to be sealed. Furthermore, adhesiveness may become manifest only on the application of a certain pressure. We prefer, nonetheless, that the desired adhesiveness be menifest at ambient temperture. Due to the preferred dual nature of the system it is also possible to adapt it easily to the appropriate application, both in terms of dimensioning and also special material properties and geometric features. Thus, a single design of seal can be used in a variety of splice cases and for a variety of cable sizes. In the design it is envisaged that the springy and/or elastic second element is substantially completely surrounded by the first element with the adhesive surface. A further layer, or surface treatment, may be provided to give the seal protection against petroleum or other fluids. The complete surrounding of the elastic and/or springy elements means that the restoring forces can act in substantially all directions. The springy element may comprise a mechanical spring, a pneumatic chamber or an elastomer, by means of which energy can be stored. The seal preferably comprises a cross-linked elastomer, more particularly an ATV or other silicon rubber, and the first and second elements may each comprise such materials, but cross-linked to different extents to produce the different properties desired. In the case of such seals various applications are known. An elastomer and/or synthetic rubber often has very favourable properties, whereby a silicon rubber vulcanised at high temperature, e.g. type MVQ, is frequently used here. In order to achieve complete cross-linking of such a material, a peroxide quota and silicic acid content of the raw material, various hardnesses of elastomers can be obtained. We have found that these materials are useful as seals, since they can exhibit low creep and low compression-set. As a result mechanical deformation is highly reversible, thus maintaining the sealing effect over time. Usually such deformability is measured in accordance with German standard DIM 53517, i.e. a pressure deformation residue is given as a yardstick after contact deformation. In addition to the crosslinked sealing materials there are other sealing materials such as non-cross-linked systems with very high viscosity and adhesiveness based on butyl rubber for instance. In the case of these materials the sealing effect maybe achieved less as a result of deformation, and more due to the surface adhesion to neighbouring surfaces, such sealing material exhibiting a restoring capability. Such sealing systems may have the disadvantage that they are less useful on components subject to great temperature variations. Nonetheless, seals having the designs required by the present invention can produce useful results with these less preferred materials. In further embodiments the invention provides a seal, which is characterised by incomplete cross-linking to give an adhesive. Preferably such a seal comprises a silicone rubber or other elastomer or other suitable material having a peroxide content of 1% or less by weight, based on the weight of cross-linkable material. In such an incompletely cross-linked elastomer seal a sufficient restoring capability remains guaranteed on the one hand, and on the other attachment of the material to the surface through the residue adhesiveness is possible. Expediently the peroxide quota lies under 0.5% by weight. For example, silicon rubber of type MVQ having various levels of peroxide was cross-linked, and we have shown that even with a peroxide quota of 0.2% adequate mechanical properties can be achieved. In particular, the required restoring force was achieved as well as an adhesiveness which allows for adequate surface adhesion to the neighbouring surfaces bordering on the seal. At this point is should be noted that not only chemical cross- linking is possible, but also physical cross-linking, e.g. through high- energy radiation. In another embodiment the invention also provides for the seal being formed of at lest two differently cross-linked layers. In this way at least one of the layers, irrespective of the type of cross-linking, be it chemical or physical, can be more, and preferably substantially completely, cross-linked. Various layer structures can be realised here or half-shells and/or other forms produced, the different layers being cross-linked to different extents. For example a partially cross-linked sealing material can be provided on the inside of a hollow seal (to seal for example to a cable passing through it) and/or on the outside (to seal to a splice case around it). The core of the material of the seal can be cross-linked to a greater extent to increase its resilience, reducing creep and allowing greater storage of energy. Further embodiments according to the invention consist in seals formed of at least two layers containing cross-linkable material, which are connected to each other and subsequently subjected to cross-linking. The seal may be formed of at least two connected layers with a varying peroxide content, whereby the overall composite is subjected to cross-linking. Alternatively, the seal maybe formed of an under-cross-linked first section and an as yet non-cross-linked second section which are connected to each other and then subjected to joint cross-linking. The invention is described below in more detail with the aid of the accompanying drawings, in which: Figure 1 shows a cable splice case with a seal of the invention; Figures 2-7 show various designs of seals; Figure 8 shows several seals, sealed to each other; Figure 9 shows a splice case with an additional sealing strip; and Figures 10-14 show embodiments of the sealing strip. Figure 1 shows a cable splice case 1 suitable for sealing splices between various types of cables (not shown). The splice case 1 comprises a base or other first part 2 and a lid or other second part 3 (each preferably moulded from a plastics material) that can be brought together by hinging etc. to form a substantially closed space around a cable splice (not shown). The cables may be for example multi-conductor copper cables, coaxial cables or optical fibre cables. The splice case may therefore accommodate conductor splice bundles, CATV splitters or taps or optical fibre splices, splitters or organiser trays. Means 4 are provided to located the splice bundles, splitters or trays etc. For example, means 4 may comprise quides within which a stack of trays may be suitably received. The splice case is shown with three inlets 5 at each end, although other configurations are possible. Each inlet may contain a seal 6 of the invention and a strain relief device 7, so that stresses on the cables are not transmitted to the seals 6 or to the connections within the splice case. The seal 6 can be seen to have a cable mating surface that is frusto-conical, thus allowing cables of different sizes to be sealed. The frusto-conical internal surface is shown ribbed, thus giving it greater flexibility. The ribs may become deformed as a cable is sealed between the seal 6 shown and a second seal (not shown) that could be secured to the lid 3 or otherwise positioned above seal 6. The seal 6 of Figure 1 is shown in greater detail in Figure 2. The seal is in the form of a complete block, the inner part of which may comprise one or more softer or tacky layers 10 preferably embedded, or provided between, harder elastomeric layers 11. The surface of the block that is to contact the cable and/or splice case housing may be coated with a gel, petroleum jelly or other suitable sealing material, or such sealing material may be an integral part of the seal. At least in the parting plane of the block, the softer layer or layers 10 preferably extend proud of the harder layer or layers 11 in order to ensure good cable sealing. This feature may be provided in the absence of other aspects of shape, and is independently inventive and useful. The block of Figure 3 is shown with its front walls removed to reveal cavities 4 that may be air-filled and may give pneumatic resilience to the seal. Even if such cavities are open (as shown), they may be advantageous in altering the resilient behaviour of the block. Figure 4 shows block parts 8, 9 which together have a convex outer surface, in this case, hexagonal, such that an externally applied compressive force (indicated by the arrows) is concentrated or focused onto a cable 15 therein. This compressive force could result from the seal being closed in an inlet 5 between the base 2 and lid 3 of a splice case such as that shown in Figure 1. Another layer of the block parts 8, 9 is preferably tacky, and the core 10 of the parts is preferably more resilient. The seal of Figure 5 comprises two parts 8, 9, each having first, 16, and second 17, cavities therein, such that the parts can be assembled with the two first partial cavities, 16, mutually aligned, as shown, or with the two second partial cavities, 17, aligned. This can allow inlets of different size to be produced from a single pair of block parts. Figure 6 shows a sealing block having an insert 18 that can be removed for use with large cables. Each of the inserts 18, and the remainder of the block may have the dual, adhesive and elastomeric, construction referred to above. The seal of Figure 7 comprises a split hollow cylinder, such that the split 20 can be opened to allow a cable to be slid laterally into hole 21. Such a split seal can of course have the overall shape shown in Figures 2 and 4 etc. In Figure 8 shows three seals sealed to each other. Each seal has a convex, 22, and a concave, 23, surface such that similar seals can be juxtaposed with the concave surface 22 of one engaging the convex surface 21 of another. Figures 10 to 14 show sealing strips 27 suitable for use around the periphery of a splice case, such as that of Figure 9. These seals may allow a sealing force applied to a splice case cover to act independently upon the cables 28 and upon the base 2 and cover 3. Preferably the sealing strips shown are substantially completely surrounded by material of the base or cover of the splice case. Sealing strips 27 may comprise a silicone rubber or other elastomer, and may be cross-linked. Alternative materials comprise gels and mastics. The dual, adhesive and elastomeric, construction described above for seal 6 may be used. The sealing strip may have a hollow core 29 such that the desired resilience is provided at least in part pneumatically. In Figure 12 a soft material 30 is located by a harder material to one side which is useful in the embodiment of Figure 11 where the sealing strip 27 abuts an inclined surface. Figures 13A and 13B show two ways in which a sealing strip 27 is retained in a recess in lid 3. Here a harder retaining core 31 is provided, with different materials 32 and 33 at its surface. Figures 14A and 14B show a sealing strip before its compression against a surface 2 to be sealed. Figure 9 shows a splice case having sliding catches 24 for holding the base 2 and the lid 3 closed. The catches 24 may have a tapered recess by means of which wedge shaped ridges on the base and lid may be forced towards one another thereby putting seals (such as seal 6 of the invention) under compression. Other means may be provided for urging first and second parts of a splice case together, thereby putting a seal under compression. The splice case is shown housing optical fibre organiser trays 25 (three are visible). The trays are located on hinges 26 by means of which they can be moved to expose the fibres on any one thereof. An elongate sealing strip 27 is provided extending substantially around the periphery of the base 2 of the splice case, to form a seal between the base 2 and the lid 3 when they are brought together. Such a sealing strip 27 may in general be provided on first and/or second parts of a splice case, and may be preinstalled in a recess for example, or may be applied when the splice case is installed. The sealing strip 27 may become sealed to the seal 6 when the first and second parts of the splice case are brought together. A seal may also, or alternatively be shaped to have one or more of the following characteristics: 1. the seal is provided in substantially block or strip form and has one or more cavities, preferably air (or other gas) filled and preferably to give pneumatic resilience to the seal; 2. the seal comprises a split hollow cylinder; and 3. the seal has a convex and a covcave surface such that similar seals can be juxtaposed with the convex surface of one engaging the concave surface of another. For the avoidance of doubt it is noted that the invention provides various shapes, constructions, materials, uses, and other aspects of designs for sealing cables and other substrates. Any one or more of the designs described or illustrated may be used in the presence or absence of any of the others, and any one or more of them may be used in a cable splice case particularly as at least part of a cable inlet.

Claims: Claims 1. A seal shaped to have one or more of the following characteristics: (a) a cable and/or housing mating surface is tapered and/or frusto-conical thus allowing cables of different sizes to be sealed within a housing of given inlet size; (b) the seal has a substantially convex outer surface, such as circular or polygonal such that externally applied compressive forces are concentrated or focused on a cable within the seal; and (c) the seal comprises two parts, each having first and second partial cavities therein, such that the parts can be assembled with the two first parts or the two second parts mutually aligned, the two first partial cavities together defining an inlet of different size or shape than the two second partial cavities together. 2. A seal according to claim 1, having an adhesive outer surface provided by a first element, and a springy or elastomeric second element, that can maintain the first element in contact with a surface to be sealed. 3. A seal according to claim 2, characterised in that the springy and/or elastic element is substantially completely surround by the first element having the adhesive surface. 4. A seal according to claim 2 or 3, characterised in that the springy element is formed by one or more of: a mechanical spring, a pneumatic chamber and an elastomer. 5. A seal according to any preceding claim, comprising a cross- linked elastomer. 6. A seal according to claim 5, in which the elastomer is incompletely cross-linked such that its surface has adhesiveness. 7. A seal according to claim 6, characterised in that it is produced by peroxide cross-linkng an elastomer having a peroxide content 1.0% or less by weight based on the weight of cross-linkable elastomer. 8. A seal according to any preceding claim which comprises a cross-linked silicone rubber. 9. A seal according to any of the preceding claims, characterised in that it is formed by bringing together at least two as yet non- crosslinked layers (2", 3") containing cross-linking agents, and then subjecting the layers to cross-linking. 10. A cable splice case incorporating a seal according to any of the preceding claims. 11. A cable splice case according to claim 10, having first and second parts that can be brought together to form a substantially closed space around a splice, the seal being compressed by the first and second parts as they are brought together. 12. A cable splice case according to claim 10 or 11, which has the seal at a cable inlet thereof, and which has a sealing strip extending substantially around a periphery of first and/or second parts of the splice case that are brought together to form a substantially closed space around a splice. 13. A cable splice case according to claim 12, in which the sealing strip becomes sealed to the seal at least when the first and second parts are brought together. 14. A seal having one or more of the following characteristics: (a) the seal is provided with substantially block or strip form and has one or more cavities, preferably air, or other gas, filled and preferably to give pneumatic resilience to the seal; (b) the seal comprises a split hollow cylinder; and (c) the seal has a convex and concave surface such that similar seals can be juxtaposed with the concave surface of one engaging the convex surface of the other. 15. A seal according to claim 14 and to any one of claims 1-13.

Inventors: FEILER GERHARD, FORTE JOERG, FREMGEN DIETER, VOCK FRANK, FEILER, GERHARD, FORTE, JOERG, FREMGEN, DIETER, VOCK, FRANK
Applicants: FEILER GERHARD, FORTE JOERG, FREMGEN DIETER, RAYCHEM LTD, ROSE WALTER GMBH & CO KG, VOCK FRANK, FEILER, GERHARD, FORTE, JOERG, FREMGEN, DIETER, RAYCHEM LIMITED, VOCK, FRANK, WALTER ROSE GMBH & CO. KG
Application year: 1994
Main classification: H02G15
IPC codes: C08K5, C08L21, C08L83, F16L57, G02B6, H02G3, H02G15